The central hypothesis of this project is that a recombinant immunoadhesin based on the coreceptor binding structure exhibited by a gp120-CD4 complex can be combined with a carrier matrix to produce a potent antiviral formulation suitable for mucosal application. We have developed a recombinant chimeric immunoadhesin based on our full- length single chain BaL gp120-CD4 complex construct (FLSC) THAT BINDS TO ccr5 and blocks R5 HIV infection (33). In order to improve the in vivo half-life of this FLSC, it was modified from the original molecule to minimize furin-mediated proteolysis (FLSC R/T) then genetically fused to the hinge-CH2-CH3 regions of human IgG1 resulting in a protein called FLSC R/T-IgG1. This molecule will be expressed, purified, and formulated in the carrier matrix called Novasomes. Novasomes are non-phospho-based liposomes that, phase 1 trials demonstrate, are safe as a vaginally applied product (Novavax IND #57,550) and that, preliminary experiments suggest, can distribute a microbicide evenly across the vaginal surface. The anti-viral activity of the FLSC R/T-IgG1/Novasome formulation will be evaluated in a PBMC-based neutralization assay against R5, X4 and X4R5 HIV isolates as well as SHIV(Ba-L), SHIV(89.6PD), and SHIV(IIIB). The dose of FLSC-IgG1 that exhibits the maximum neutralizing efficacy with the minimum cellular toxicity when formulated with Novasomes will be selected for safety assessment. The lead FLSC R/T-IgF1/Novasomes mixture and a formulation containing a 10-fold lower dose of FLSC R/T- IgG will be evaluated in the rabbit vaginal irritation model, a vaginal irritation testing method suggested by the Food and Drug Administration. The formulation that exhibits the best safety profile in this model will be evaluated next in rhesus macaques. Vaginal surfaces of treated rhesus macaques will be visually examined for signs of irritation and inflammation. Tissue biopsies will be retrieved after the application and examined for infiltrates. The FLSC R/T-IgG1/Novasomes formulation that exhibits the highest efficacy against HIV and SHIV, minimum cellular toxicity, and best safety profile in both rabbits and rhesus macaques will be used in challenge study outlined in Project 3.